add model usage, citation, reference

model_zoo/TMKD/README.md

@@ -5,4 +5,37 @@ Source model for WSDM 2020 paper "[Model Compression with Two-stage Multi-teache
 The link to the pre-trained model:
 - [TMKD-Stage1-small-uncased](https://drive.google.com/open?id=1PUr1UOKWpUlsIqAMLnRzXxaOPhfXerVe): 3-layer, 768-hidden,12-heads
 
+## Usage
+You can use [Transformers](https://github.com/huggingface/transformers) code repo to load our stage1 model weights directly. 
 
+## Citation
+For more information, our work is helpful to you, please kindly cite our paper as follows:
+```
+@inproceedings{DBLP:conf/wsdm/YangSGLJ20,
+  author    = {Ze Yang and
+               Linjun Shou and
+               Ming Gong and
+               Wutao Lin and
+               Daxin Jiang},
+  editor    = {James Caverlee and
+               Xia (Ben) Hu and
+               Mounia Lalmas and
+               Wei Wang},
+  title     = {Model Compression with Two-stage Multi-teacher Knowledge Distillation
+               for Web Question Answering System},
+  booktitle = {{WSDM} '20: The Thirteenth {ACM} International Conference on Web Search
+               and Data Mining, Houston, TX, USA, February 3-7, 2020},
+  pages     = {690--698},
+  publisher = {{ACM}},
+  year      = {2020},
+  url       = {https://doi.org/10.1145/3336191.3371792},
+  doi       = {10.1145/3336191.3371792},
+  timestamp = {Fri, 24 Jan 2020 12:03:51 +0100},
+  biburl    = {https://dblp.org/rec/conf/wsdm/YangSGLJ20.bib},
+  bibsource = {dblp computer science bibliography, https://dblp.org}
+}
+```
+
+### Reference
+* [Transformers](https://github.com/huggingface/transformers)
+* [HuggingFace's Transformers: State-of-the-art Natural Language Processing](https://arxiv.org/abs/1910.03771)